using System;
/*
 * Copyright 2007 ZXing authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

namespace iTextSharp.text.pdf.qrcode {

    /**
     * <p>Encapsulates a QR Code's format information, including the data mask used and
     * error correction level.</p>
     *
     * @author Sean Owen
     * @see ErrorCorrectionLevel
     */
    public sealed class FormatInformation {

        private const int FORMAT_INFO_MASK_QR = 0x5412;

        /**
         * See ISO 18004:2006, Annex C, Table C.1
         */
        private static readonly int[][] FORMAT_INFO_DECODE_LOOKUP = {
            new int[]{0x5412, 0x00},
            new int[]{0x5125, 0x01},
            new int[]{0x5E7C, 0x02},
            new int[]{0x5B4B, 0x03},
            new int[]{0x45F9, 0x04},
            new int[]{0x40CE, 0x05},
            new int[]{0x4F97, 0x06},
            new int[]{0x4AA0, 0x07},
            new int[]{0x77C4, 0x08},
            new int[]{0x72F3, 0x09},
            new int[]{0x7DAA, 0x0A},
            new int[]{0x789D, 0x0B},
            new int[]{0x662F, 0x0C},
            new int[]{0x6318, 0x0D},
            new int[]{0x6C41, 0x0E},
            new int[]{0x6976, 0x0F},
            new int[]{0x1689, 0x10},
            new int[]{0x13BE, 0x11},
            new int[]{0x1CE7, 0x12},
            new int[]{0x19D0, 0x13},
            new int[]{0x0762, 0x14},
            new int[]{0x0255, 0x15},
            new int[]{0x0D0C, 0x16},
            new int[]{0x083B, 0x17},
            new int[]{0x355F, 0x18},
            new int[]{0x3068, 0x19},
            new int[]{0x3F31, 0x1A},
            new int[]{0x3A06, 0x1B},
            new int[]{0x24B4, 0x1C},
            new int[]{0x2183, 0x1D},
            new int[]{0x2EDA, 0x1E},
            new int[]{0x2BED, 0x1F}
        };

        /**
         * Offset i holds the number of 1 bits in the binary representation of i
         */
        private static readonly int[] BITS_SET_IN_HALF_BYTE =
            { 0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4 };

        private ErrorCorrectionLevel errorCorrectionLevel;
        private byte dataMask;

        private FormatInformation(int formatInfo) {
            // Bits 3,4
            errorCorrectionLevel = ErrorCorrectionLevel.ForBits((formatInfo >> 3) & 0x03);
            // Bottom 3 bits
            dataMask = (byte)(formatInfo & 0x07);
        }

        public static int NumBitsDiffering(int a, int b) {
            a ^= b; // a now has a 1 bit exactly where its bit differs with b's
            // Count bits set quickly with a series of lookups:
            return BITS_SET_IN_HALF_BYTE[a & 0x0F] +
                BITS_SET_IN_HALF_BYTE[(a >> 4 & 0x0F)] +
                BITS_SET_IN_HALF_BYTE[(a >> 8 & 0x0F)] +
                BITS_SET_IN_HALF_BYTE[(a >> 12 & 0x0F)] +
                BITS_SET_IN_HALF_BYTE[(a >> 16 & 0x0F)] +
                BITS_SET_IN_HALF_BYTE[(a >> 20 & 0x0F)] +
                BITS_SET_IN_HALF_BYTE[(a >> 24 & 0x0F)] +
                BITS_SET_IN_HALF_BYTE[(a >> 28 & 0x0F)];
        }

        /**
         * @param maskedFormatInfo1 format info indicator, with mask still applied
         * @param maskedFormatInfo2 second copy of same info; both are checked at the same time
         *  to establish best match
         * @return information about the format it specifies, or <code>null</code>
         *  if doesn't seem to match any known pattern
         */
        public static FormatInformation DecodeFormatInformation(int maskedFormatInfo1, int maskedFormatInfo2) {
            FormatInformation formatInfo = DoDecodeFormatInformation(maskedFormatInfo1, maskedFormatInfo2);
            if (formatInfo != null) {
                return formatInfo;
            }
            // Should return null, but, some QR codes apparently
            // do not mask this info. Try again by actually masking the pattern
            // first
            return DoDecodeFormatInformation(maskedFormatInfo1 ^ FORMAT_INFO_MASK_QR,
                                             maskedFormatInfo2 ^ FORMAT_INFO_MASK_QR);
        }

        private static FormatInformation DoDecodeFormatInformation(int maskedFormatInfo1, int maskedFormatInfo2) {
            // Find the int in FORMAT_INFO_DECODE_LOOKUP with fewest bits differing
            int bestDifference = int.MaxValue;
            int bestFormatInfo = 0;
            for (int i = 0; i < FORMAT_INFO_DECODE_LOOKUP.GetLength(0); i++) {
                int[] decodeInfo = FORMAT_INFO_DECODE_LOOKUP[i];
                int targetInfo = decodeInfo[0];
                if (targetInfo == maskedFormatInfo1 || targetInfo == maskedFormatInfo2) {
                    // Found an exact match
                    return new FormatInformation(decodeInfo[1]);
                }
                int bitsDifference = NumBitsDiffering(maskedFormatInfo1, targetInfo);
                if (bitsDifference < bestDifference) {
                    bestFormatInfo = decodeInfo[1];
                    bestDifference = bitsDifference;
                }
                if (maskedFormatInfo1 != maskedFormatInfo2) {
                    // also try the other option
                    bitsDifference = NumBitsDiffering(maskedFormatInfo2, targetInfo);
                    if (bitsDifference < bestDifference) {
                        bestFormatInfo = decodeInfo[1];
                        bestDifference = bitsDifference;
                    }
                }
            }
            // Hamming distance of the 32 masked codes is 7, by construction, so <= 3 bits
            // differing means we found a match
            if (bestDifference <= 3) {
                return new FormatInformation(bestFormatInfo);
            }
            return null;
        }

        public ErrorCorrectionLevel GetErrorCorrectionLevel() {
            return errorCorrectionLevel;
        }

        public byte GetDataMask() {
            return dataMask;
        }

        public int HashCode() {
            return (errorCorrectionLevel.Ordinal() << 3) | (int)dataMask;
        }

        public override int GetHashCode() {
            return base.GetHashCode();
        }

        public override bool Equals(Object o) {
            if (!(o is FormatInformation)) {
                return false;
            }
            FormatInformation other = (FormatInformation)o;
            return this.errorCorrectionLevel == other.errorCorrectionLevel &&
                this.dataMask == other.dataMask;
        }
    }
}